<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>天气案例</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
     <!--准备好一个容器-->
     <div id="root">
           姓:<input type="text"  v-model="firstName"> <br/><br/>
           名:<input type="text" v-model="lastName"><br/><br/>
           全名:<span>{{fullName}}</span> <br/><br/>
     </div>
</body>
  <script>
    Vue.config.productionTip = false //阻止 vue 在启动时生成生产提示。

     const vm =  new Vue({
        el:'#root',
        data:{
            firstName:'张',
            lastName:'三',
            fullName:'张一三'
        },
        watch:{
            firstName(val){
                setTimeout(()=>{
                    console.log(this)
                    this.fullName = val +'-'+this.lastName
                },2000);
            },
            lastName(val){
                this.fullName = this.firstName+'-'+val
            }
        }
      })
  </script>
</html>